1. Field of the Invention
The present invention relates generally to a video signal processing circuit used in performing vibration correction for a video camera and, more particularly, to providing defective pixel compensation and optical detector window adjustment in accordance with the vibration correction.
2. Description of the Background
In recent years, the realization of a miniature light-weight video camera has progressed and today such a video camera can be fairly easily handled. On the other hand, in association with the miniaturization and lowered weight of the video camera, the video camera can be so easily moved that the photographing operation is readily influenced by camera movement and vibration. A video camera, therefore, having a vibration correcting feature has been proposed and put into practical use.
As a vibration correcting system for a video camera, there has been proposed a circuit in which an image pickup signal from an image pickup device is stored in a field memory, and the picture plane is enlarged and interpolated in the field memory. The reading out operation from the field memory is controlled in accordance with the vibration of the camera, and the vibration is corrected. Such a system is disclosed in U.S. patent application Ser. No. 673,783 assigned to the assignee of the instant application. Nevertheless, when the picture plane is enlarged and interpolated as described above, the resolution deteriorates.
There has also been proposed a mechanism in which a variable optical axis prism is arranged in front of a lens, the prism is moved in accordance with the vibrations of the camera, the refraction angle of the incident light is changed, and the vibration is compensated. Such a system is disclosed in Japanese patent application number Hei 04-016968. According to such a vibration correcting mechanism, because the picture plane is not enlarged and interpolated, the picture quality is not deteriorated. Nevertheless, according to such a vibration correcting mechanism the variable optical axis prism must be mechanically moved. Therefore, the required mechanical structure becomes an obstacle to realizing a small sized and light-weight camera.
Further, there has been proposed a system in which the image pickup device of the camera has a number of lines greater than the number of lines of the standard television system, the picture plane is vertically moved by using the surplus lines which are available, and the vibration is corrected. This system is disclosed in U.S. patent application Ser. No. 978,366 also assigned to the assignee of the instant application.
In this latter system, for instance, a CCD image pickup device of the PAL system is used to output the video signal of the NTSC system. When the video signal of the NTSC system is generated by using the CCD image pickup device of the PAL system, because the number of lines of the PAL system is greater than the number of lines of the NTSC system, surplus lines are provided. The number and location of the lines in the CCD image pickup device is transferred at a high speed during the vertical blanking period. By changing the number of lines in the high-speed transfer with respect to the number of lines before and after the video frame time, the picture plane can be vertically moved.
Nevertheless, when such a vibration correction using an increase in CCD lines is executed, the high-speed transfer is executed during the blanking period, so that considerably large charges must flow from a vertical transfer register into a horizontal transfer register of the CCD image pickup device. Consequently, there occurs the problem that when a strong light is irradiated onto the CCD image pickup device, the charge amount exceeds the capacity of the horizontal transfer register and the overflow charges reverse flow into the vertical transfer register side.
Moreover, as a practical matter defective pixels are always included in the pixels of a CCD image pickup device. Hitherto, position information of the defective pixels is stored in a memory and processes such as interpolation and the like are executed at the positions of the defective pixels, thereby coping with the defective pixels.
As described above, when the image pickup device having a number of lines greater than the number of lines of the standard television system is used vibration correction is executed by vertically moving the picture plane by using the surplus lines which are available. Therefore, because the defective pixel information is fixed as addresses in a memory, when the video signal is moved to perform vibration correction the positions of the defective pixels do not correspond to the positions at which the defect correction is to be executed.
When the image pickup device in which the number of lines is larger than the number of lines of the standard television system is used, the vertical height of the image pickup picture plane is increased. Therefore, the image pickup signal is stored in a line memory and is time-base converted in accordance with a magnification ratio. By such time-base converting the image pickup signal, the picture plane is enlarged in the horizontal direction. Therefore, by shifting the enlarged picture plane in accordance with a vibration amount in the horizontal direction, the vibration in the horizontal direction can be corrected.
In performing the time-base conversion by using the line memory as mentioned above, there is considered a method whereby a write clock signal, and a read clock signal are set to the same clock and the same data is read out a plurality of times in accordance with the magnification ratio. After such multiple read out, the data is interpolated by an interpolation filter, however, when the interpolation filter is used the picture quality deteriorates.
Some video cameras have a window to detect optical information for performing automatic exposure control and automatic focus control. For example, automatic exposure control is executed by detecting a video signal level using the detection window and by setting an opening amount of an iris and a gain of an automatic gain control circuit (AGC) in accordance with the video signal level. As mentioned above, when the image pickup signal is stored in the line memory, the picture plane is enlarged in the horizontal direction, the enlarged picture plane is shifted in accordance with a vibration amount in the horizontal direction, and the vibration in the horizontal direction is corrected. Thus, the position of the window is deviated relative to the position of an object to be photographed. For example, when the position of the window coincides with the position over the object or is moved away therefrom due to vibration, although the amount of light in the window changes, the photographed picture plane is stationary due to the vibration correction. Therefore, a phenomenon occurs in which the brightness changes in spite of the fact that the picture plane is stationary.